feat(alerts): 🎉 Add alert for high disk consumption in Forgejo

Add a new alert for monitoring high disk consumption in the Forgejo environment.

This alert triggers when disk usage exceeds 60% for persistent volume claims, enhancing observability and proactive resource management in the cluster.

otc/observability.t09.de/stacks/observability/victoria-k8s-stack/manifests/alerts.yaml

@@ -27,3 +27,14 @@ spec:
           annotations:
             value: "{{ $value }}"
             description: 'forgejo s3 backup job failed in cluster environment {{ $labels.cluster_environment }}'
+    - name: forgejo-disk-consumption
+      rules:
+        - alert: forgejo disk consumption high
+          expr: 1-(kubelet_volume_stats_available_bytes / kubelet_volume_stats_capacity_bytes) > 0.6
+          for: 30s
+          labels:
+            severity: major
+            job:  "{{ $labels.job }}"
+          annotations:
+            value: "{{ $value }}"
+            description: 'disk consumption of pvc {{ $labels.namespace }}/{{ $labels.persistentvolumeclaim }} is high in cluster environment {{ $labels.cluster_environment }}'